The present invention relates to a ceramic sheathed element glow plug for diesel engines. Such a sheathed element glow plug is already described in German Patent 3 837 128, where a ceramic heating device is held by the tip of a cylindrical holder. The ceramic heating device is thus electrically insulated with respect to the holder. A terminal device contacting the power supply voltage is provided on the side of the cylindrical holder opposite the ceramic heating device. The ceramic heating device includes a U-shaped heating section, with the two ends of the U-shaped heating section contacting the terminal device by wires or terminals sintered in place. During glow operation, a voltage is applied to the ceramic heating device, so that a current flows from one end of the U-shaped heating section over the tip of the heating section facing the combustion chamber to the other end of the U-shaped heating section. Because of the resistance of the ceramic, the current causes the heating section to heat up so that it glows, and the fuel-air mixture for ignition is heated.
The ceramic sheathed element glow plug according to the present invention has the advantage that by inserting a ceramic bushing and a ring into the plug casing, the latter is filled and is thus more stable, and in assembly of the sheathed element glow plug, a sealing compound provided between the end of the plug casing remote from the combustion chamber and the ceramic heating device can be compressed well. The pressure applied from the opening remote from the combustion chamber is transferred well over the ring and the ceramic bushing to the ceramic heating device, guaranteeing the desired seating of the ceramic heating device in the metal casing. Production is ultimately simplified and therefore is less expensive.
It is especially advantageous that first a ceramic bushing is arranged in the plug casing following the ceramic heating device. Good insulation of the inner conductor arrangement which passes centrally through the ceramic bushing is thus provided at the same time. Moreover, the ceramic bushing may sit directly on the ceramic heating device. Use of a ring such as a metal ring which is not sensitive to shock has the advantage that point pressure applied to the metal ring in assembly of the sheathed element glow plug is distributed well over the metal ring on the entire surface area of the ceramic bushing and the end face of the ceramic heating device remote from the combustion chamber. Due to the two-dimensional distribution of the applied compression pressure, the stress load on the ceramic is minimized.